Biting, gnawing, glinting, cold

I sit here, in front of you. I can be used for so many purposes. Most use me more for practical reasons, their food, their items, their care. However, anything can be used for evil, and I am no exception. I may use my frigid but steel-like nature to bite and grind into someone or something. My nature can change in an instant. I could gnaw through some cheese, or I could tear into flesh with thick red liquid as my reward. It is your choice, what shall you use me for?